1. Field of the Invention
This invention relates to a method for generating frame lines in an image displaying or recording system using raster scanning means, and more particularly to a method for generating frame lines together with character data to be displayed or recorded in an image scanning system like a COM (computer output microfilmer).
2. Description of the Prior Art
In an image scanning system like a COM, the output data of a computer or the like are often recorded or displayed on a recording medium or a display device together with a format like a frame of table or the like as shown in FIG. 1. In order to display or record the output data of the computer or the like together with the format, various methods have been put into practical use as follows.
The first method uses a transparency recorded with the format. The format recorded on the transparency is optically projected on the recording medium and recorded on the recording medium together with the output data directly recorded thereon by means of a scanning light beam. This method is advantageous in case that the sensitivity of the recording medium is low, for example in case of a heat mode recording material to be recorded with a laser beam, in that the recording of the format does not need high sensitivity of the recording medium. However, on the other hand, this method is disadvantageous in that the amount of light or energy of the light to be used for projecting the image of the format must be great enough to record the image on the low sensitivity recording medium.
The second method uses a master format slide or the like to be scanned with a laser beam. The laser beam used for recording the output data is also modulated with respect to the format information in accordance with the transmittivity or reflectivity of the format slide, whereby the format is recorded on the recording medium together with the output data by means of the recording laser beam. This method is disadvantageous in that the format is not recorded with high accuracy. This is because there are errors in parallelism of scanning lines, straightness of scanning lines, diameter of scanning light spot and threshold level of sensors and accordingly the straight thin lines of the format are not read out and/or recorded as straight thin lines. Consequently, the straight thin lines are recorded as disaligned straight lines or curved or waved lines or thick lines or sometimes are not recorded at all.
The third method uses electronically memorized format similarly to the method of recording graphic characters. This method is devided into two kinds as follows. In the first kind, format data are generated in synchronization with the ordinary character data by use of a read only memory for a pattern generator called format line font memory and a frame memory which memorizes format line data for one frame in terms of a code. In the second kind, format data are generated in synchronization with the ordinary character data by use of a frame memory which memorizes format line data for one frame as a dot pattern as a whole.
These two kinds of methods of the third method need a great capacity of the frame memory. For example, in case that one frame involves 160 characters in a horizontal line and 86 characters in a vertical line and each character is formed with 9.times.16 dots (7.times.9 dots for the character and the remainder for the space), the frame memory needs the capacity of
8.times.160.times.86=110,080 bits in the first kind where the format line font memory has 256 kinds (8 bits), and PA1 9.times.16.times.160.times.86=1,981,440 bits in the second kind. Though the first kind appears not to need so much capacity as the second kind, the first kind needs the font memory in addition. Accordingly, both the first and second kinds need a great capacity of memory.